A Stress Gradient-enhanced Piezoelectric Actuator Composite (GEPAC) with Integrated Ultrasonic NDE Capability for Continuous Health Monitoring

Abstract

Stress gradient-enhanced piezoelectric actuator composites (GEPACs) are unimorph, curved actuators that can be used as low-frequency actuators embedded, for instance, within an aircraft skin. The actuator is made of a thin PZT ceramic layer bonded between two composite layers with different coefficients of thermal expansion. These curved actuators provide large bending motion. Actuators have been manufactured with segmented upper electrodes so that they can also be used at ultrasonic frequencies to monitor continuously the integrity of the actuator itself. It is shown that the actuator can be used to detect interfacial defects such as debonding between the piezoelectric layer and the outer layers. The input signal is a one-cycle burst at 1 MHz. The time domain signals recorded experimentally are compared with predictions from a finite element model. It is shown that the presence of a debonding defect can convert a symmetric pulse into a primarily antisymmetric wave. A simple correlation technique is used to estimate the size of the debonding region.